1. Field of the Invention
The present invention relates to a weather-sealing structure of a lens barrel which prevents water, dust and the like from entering inside the lens barrel via a gap between annular members of the lens barrel.
2. Description of the Prior Art
Lens barrels such as photographic lenses for use in cameras usually include a plurality of annular members which are concentrically arranged to be movable relative to each other along an optical axis and/or to be rotatable relative to each other about an optical axis. In the case where one of the plurality of annular members is either a hand-operated zoom ring or a hand-operated focus ring, so that manually rotating the zoom ring or the focus ring forward and reverse causes another annular member to move forward and rearward along the optical axis, it has been conventional practice to make adjacent annular members (which are overlaid radially) of the plurality of annular members produce friction therebetween intentionally so that the user can feel a moderate rotational resistance in the zoom ring or the focus ring when manually rotating the zoom ring or the focus ring.
As an example of a device which produces such a resistance, an annular friction member made of synthetic leather which is provided with fine and minute hairs implanted entirely into one of the radially outer and inner surfaces of the annular friction member is used, wherein the other of the radially outer and inner surfaces of the annular friction member is fixed to one of the radially adjacent surfaces (inner and outer peripheral surfaces) of the aforementioned adjacent annular members while the hair-implanted surface of the annular friction member is made to be in contact with the other of the radially adjacent surfaces of the aforementioned adjacent annular members to be slidable thereon.
However, although the lens barrel is configured so that the user can feel a moderate rotational resistance in the zoom ring or the focus ring if a synthetic leather member is adopted in this manner, it is difficult to prevent water, dust and the like from entering inside the lens barrel from a gap between the aforementioned adjacent annular members (i.e., to make the lens barrel weather-resistant).
A lens barrel which is constructed so that the user can feel a moderate rotational resistance in the zoom ring or the focus ring when manually rotating the zoom ring or the focus ring, while providing a weather-sealing structure, is known in the art, and an example of such a lens barrel is disclosed in Japanese unexamined patent publication 2000-227534 (hereinafter referred to as Patent Publication 1).
In the lens barrel disclosed in Patent Publication 1, annular washers 7 and 8 made of a material such as a plastic or polychloroethene sheet are inserted in between a rear end portion of an outer peripheral surface of a front exterior ring 3 and a front end portion of an inner peripheral surface of a manual operation ring 4 which is positioned immediately behind the front exterior ring 3 to be rotatable relative to the front exterior ring 3 about the optical axis (and to be prevented from moving in the optical axis direction relative to the front exterior ring 3), and annular washers 11 and 12 made of a material such as a plastic or polychloroethene sheet are inserted in between the rear end portion of the outer peripheral surface of the manual operation ring 4 and the front end portion of the inner peripheral surface of a rear exterior ring 9 which is positioned immediately behind the manual operation ring 4. Additionally, a water repellent is filled into a gap between the rear end portion of the outer peripheral surface of the front exterior ring 3 and the front end portion of the inner peripheral surface of the manual operation ring 4 to be positioned immediately behind the annular washers 7 and 8, and a water repellent is filled into a gap between the rear end portion of the outer peripheral surface of the manual operation ring 4 and the front end portion of the inner peripheral surface of the rear exterior ring 9 to be positioned immediately before the annular washers 11 and 12.
In the lens barrel disclosed in Patent Publication 1 that has the above described configuration, the annular washers 7, 8, 11 and 12 and the front and rear water repellents utilize the weather-sealing capabilities thereof, thus preventing water and dust from entering inside the lens barrel. Moreover, since the annular washers 7 and 8 are held between the front exterior ring 3 and the manual operation ring 4 while the annular washers 11 and 12 are held between the manual operation ring 4 and the rear exterior ring 9, the user can feel a moderate rotational resistance in the manual operation ring 4 when manually rotating the manual operation ring 4.
However, in the lens barrel disclosed in Patent Publication 1, since the annular washers 7, 8, 11 and 12 are formed of a relatively hard plastic or polychloroethene sheet, it is difficult to make the user feel a rotational resistance in the manual operation ring 4 in a manner similar to the manner in the case of adopting the aforementioned friction member made of synthetic leather. Specifically, in the case where an annular member rotates about an optical axis while sliding along the optical axis, it is more difficult to make the user feel a rotational resistance in a manual operation ring (such as the manual operation ring 4) in a manner similar to the manner in the case of adopting the aforementioned friction member made of synthetic leather than the case where an annular member only slides along an optical axis or only rotates about an optical axis.
Additionally, since the annular washers 7, 8, 11 and 12 are made of a relatively hard plastic or polychloroethene sheet, if minute knurls (pits and projections) exist on surfaces of the annular washers 7, 8, 11 and 12, there is a possibility that the manual operation ring 4 may not be manually rotated smoothly due to the influence of such minute knurls. Accordingly, the annular washers 7, 8, 11 and 12 need to be formed precisely with specification requirements; however, it is difficult to form the annular washers 7, 8, 11 and 12 out of a relatively hard plastic or polychloroethene sheet precisely.